GStreamer UDP receive buffer (8 MB) fails without net.core.rmem_max privilege

[DonLakeFlyer]

Problem

When receiving UDP video streams, QGC explicitly sets an 8 MB socket receive buffer on the GStreamer udpsrc element (GstVideoReceiver.cc line 761):

g_object_set(source,
             "uri", uri.toUtf8().constData(),
             "buffer-size", 8 * 1024 * 1024,  // 8388608 bytes
             nullptr);

GStreamer passes this value to setsockopt(SO_RCVBUF, 8388608). On Linux, the kernel rejects this if the process lacks CAP_NET_ADMIN and net.core.rmem_max is below 8 MB (the default is ~208 KB on most distros).

Symptoms

The following warnings appear in the QGC log:

Could not create a buffer of requested 8388608 bytes (Operation not permitted). Need net.admin privilege? - Video.GStreamer.GstVideoReceiver
GStreamer warning: Could not get/set settings from/on resource. debug: ../gst/udp/gstudpsrc.c: gst_udpsrc_open(): /GstPipeline:receiver/GstBin:sourcebin/GstUDPSrc:source

Impact

The UDP pipeline still starts, but with the kernel's default receive buffer. Under high-bitrate or high-latency conditions, the small buffer fills up before the app can read it, resulting in UDP packet drops and degraded video quality.

Fix / Workaround

Raise the kernel socket receive buffer limit:

# Permanent fix
echo "net.core.rmem_max=8388608" | sudo tee /etc/sysctl.d/99-udp-rmem.conf
sudo sysctl -p /etc/sysctl.d/99-udp-rmem.conf

Consider also:

• Documenting this requirement in the Linux install/setup guide.
• Falling back gracefully and logging a clear user-facing message when the buffer size cannot be set.

[DonLakeFlyer]

This is happening in my Linux 24.04 VM

[HTRamsey]

Yup this is a long time bug